1. Field of the Invention
This invention relates in general to earth boring bits, particularly to those utilizing diamonds for cutting elements used to disintegrate geological formations.
2. Description of the Prior Art
Commercially available earth boring bits can be generally divided into the rolling cutter bits, having either steel teeth or tungsten carbide inserts, and diamond bits, which utilize either natural diamonds or artificial or man-made diamonds. The artificial diamonds are "polycrystalline", used either individually or as a component of a composite compact or insert on a cemented tungsten carbide substrate. Recently, a new artificial, polycrystalline diamond has been developed which is stable at higher temperatures than the previously known polycrystalline diamond. Both types of polycrystalline diamond are available in a wide variety of shapes and sizes.
The diamond earth boring bits can be generally classified as either steel bodies bits or matrix bits. The steel bodied bits are machined from a steel block and typically have cutting elements which are press-fit into recesses provided in the bit face. The matrix bit is formed by coating a hollow tubular steel mandrel in a casting mold with metal bonded hard material, such as tungsten carbide. The casting mold is of a configuration which will give a bit of the desired form. The cutting elements are typically either polycrystalline diamond compact cutters brazed within a recess provided in the matrix backing or are thermally stable polycrystalline diamond cutters which are cast within recesses provided in the matrix backing.
Placement of the cutter elements on the bit face of matrix bits has fallen into two general schemes. In the first of these, the cutters are placed in a straight row extending from a central location on the bit face out to the full bit diameter. The performance of these bits is sometimes limited by the fact that cuttings dislodged at the center of the bit face must move in a straight line down the cutting blade before exiting the bit face. There is a tendency for cuttings to collect on the bit face and restrict fluid flow across the bit face. In addition, cuttings from the bit center are reground along the entire length of the blade, accelerating wear.
In the second scheme, cutters are set in individual mountings placed strategically around the bit face. These bits are disadvantaged by the fact that individual cutter mounts are more susceptible to gross failure by shearing.